laws, and the practice of power-sharing between several kings simultaneously, gave personal conflicts the potential to become full-blown wars. More recently historian Narve Bjørgo has suggested that the practice of power-sharing was actually a good way of governing the kingdom in the first period after its unification, and that tendencies towards centralization, and a unitary kingdom, were important factors in triggering the wars. Edvard Bull has also emphasized geographical animosities as a factor, pointing to the fact that different pretenders often found their main support in certain parts of the country. Also important was the involvement of foreign powers: Danish and, to a lesser extent, Swedish kings were always ready to lend their support to factions in the Norwegian wars, with an eye to extending their own influence, particularly in the Viken (Oslofjord) area. A popular explanation in early Norwegian historiography (late 19th, early 20th century) was a conflict between the royal power and the aristocracy (the lendmenn). According to this view, by historians such as P.A. Munch, J.E. Sars and Gustav Storm, the aristocracy saw the king as a tool by which they governed the country. Consequently, they supported weak kings but were eventually beaten by the strong king Sverre. The same views are expounded concerning the involvement of the Church. These explanations lost credence as it became clear that the lendmenn seemed to be evenly split on different sides, both before and after King Sverre. Sverre himself even had some of the lendmenn on his side. Knut Helle has emphasised how the Church, after Sverre's death, seemed to work hard to bring about reconciliation between warring parties, and stability. Towards the middle of the 20th century historical materialism gained much popularity in Norwegian historiography. Its proponents, e.g. Edvard Bull and Andreas Holmsen, sought to explain the civil wars on a social and economic basis. They assumed that Norwegian society became more stratified in the 12th century, with large groups of previously self-owning farmers sinking to the status of tenant-farmers, while the lendmenn and the Church amassed great landholdings. This created conflicts which found an outlet in the civil wars. There is also an assumption that certain regions, such as Trøndelag and inner parts of eastern Norway, were more egalitarian and therefore opposed the more stratified regions of the country. These attempts to introduce a form of class struggle-explanation to the conflicts have lost ground more recently, as they